my brother stopped over with an issue that i have no idea this was normal. he told me the battery gage in the dash after he starts the truck goes up to 14+ volts and then it drops down to like 12+ volts.

so i took it and hooked up my scanner as the volts goes up to 14.9 and then in a minute or so drops to 12.6 and stays there. so i did some tests i connected my alt test meter and it said the system was good so i did the voltmeter at the battery posts and it was 14.9 then dropped to 13.6 and never got below that during my test at the battery posts. so i did ohms from the battery post to the back of the alt and i had 0.00 ohms and the same for the ground to the stud on the block and had 0.00 ohms that tells me the connections are good.

so is this a normal thing he is seeing? i took the alt off and ohmed the diodes and had ,487 about that anyway across all the diodes. and 0.00 ohms from a diode to the rectifier unit, but i have no meter to test the rectifier.
i did find the brushes worn out so i put new brushes in it and he said he still has the same thing. so now he did get a new alt but but we have not yet installed that, but if this is a normal reading at the battery gage then there is no sense putting on the new alt and then have the same thing happen. he then pays 250$ for the same readings.

so can anyone tell me if what he is seeing is a normal reading at the dash gage? also that gage is not fast getting to the readings it moves slow enough but that may be the way gm set them up.

thanks